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Date:   Mon, 22 Feb 2021 03:27:25 +0200
From:   Laurent Pinchart <laurent.pinchart@ideasonboard.com>
To:     Jacopo Mondi <jacopo+renesas@jmondi.org>
Cc:     kieran.bingham+renesas@ideasonboard.com,
        niklas.soderlund+renesas@ragnatech.se, geert@linux-m68k.org,
        Mauro Carvalho Chehab <mchehab@kernel.org>,
        linux-media@vger.kernel.org, linux-renesas-soc@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 09/16] media: i2c: rdacm21: Re-work OV10640 initialization
Message-ID: <YDMIfTtc7ottA6Ir@pendragon.ideasonboard.com>
References: <20210216174146.106639-1-jacopo+renesas@jmondi.org>
 <20210216174146.106639-10-jacopo+renesas@jmondi.org>
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In-Reply-To: <20210216174146.106639-10-jacopo+renesas@jmondi.org>
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Hi Jacopo,

Thank you for the patch.

On Tue, Feb 16, 2021 at 06:41:39PM +0100, Jacopo Mondi wrote:
> The OV10640 image sensor reset and powerdown on signals are controlled

s/ on//

> by the embedded OV490 ISP. The current reset procedure does not respect
> the 1 millisecond power-up delay and releases the reset signal before
> the powerdown one.
> 
> Fix the OV10640 power up sequence by releasing the powerdown signal,
> waiting the mandatory 1 millisecond power up delay and then releasing
> the reset signal. The reset delay is not characterized in the chip
> manual if not as "255 XVCLK + initialization". Wait for at least 3
> milliseconds to guarantee the SCCB bus is available.
> 
> This commit fixes a sporadic start-up error triggered by a failure to
> read the OV10640 chip ID:
> rdacm21 8-0054: OV10640 ID mismatch: (0x01)
> 
> Signed-off-by: Jacopo Mondi <jacopo+renesas@jmondi.org>
> ---
>  drivers/media/i2c/rdacm21.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/media/i2c/rdacm21.c b/drivers/media/i2c/rdacm21.c
> index b22a2ca5340b..c420a6b96879 100644
> --- a/drivers/media/i2c/rdacm21.c
> +++ b/drivers/media/i2c/rdacm21.c
> @@ -333,13 +333,15 @@ static int ov10640_initialize(struct rdacm21_device *dev)
>  {
>  	u8 val;
>  
> -	/* Power-up OV10640 by setting RESETB and PWDNB pins high. */
> +	/* Power-up OV10640 by setting PWDNB and RESETB pins high. */
>  	ov490_write_reg(dev, OV490_GPIO_SEL0, OV490_GPIO0);
>  	ov490_write_reg(dev, OV490_GPIO_SEL1, OV490_SPWDN0);
>  	ov490_write_reg(dev, OV490_GPIO_DIRECTION0, OV490_GPIO0);
>  	ov490_write_reg(dev, OV490_GPIO_DIRECTION1, OV490_SPWDN0);
> -	ov490_write_reg(dev, OV490_GPIO_OUTPUT_VALUE0, OV490_GPIO0);
> +
>  	ov490_write_reg(dev, OV490_GPIO_OUTPUT_VALUE0, OV490_SPWDN0);

Shouldn't this be OV490_GPIO_OUTPUT_VALUE1 ?

> +	usleep_range(1500, 3000);
> +	ov490_write_reg(dev, OV490_GPIO_OUTPUT_VALUE0, OV490_GPIO0);

I'm a bit puzzled by why this patch would improve the ID read issue,
given that it sets GPIO0 to 1, then sets GPIO0 to 1, compared to
previously setting GPIO0 to 1 following by setting GPIO0 to 1 :-) Maybe
it's the additional delay ? In any case, it would probably be a good
idea to perform additional tests after fixing this.

>  	usleep_range(3000, 5000);
>  
>  	/* Read OV10640 ID to test communications. */

-- 
Regards,

Laurent Pinchart